Pedicle screw based vertebral body stabilization apparatus

ABSTRACT

A pedicle screw stabilization device comprises a superior and inferior pedicle screw anchor with a shaped memory alloy spacer therebetween.

FIELD OF THE INVENTION

The present invention relates to vertebral body stabilization and support and, more particularly, to a pedicle screw based system providing flex restrictions on vertebral bodies.

BACKGROUND OF THE INVENTION

Surgical techniques to correct or address spinal problems are turning more and more to non-fusion technologies. One type technology involves spinous process stabilization. Spinous process stabilization is further explained in U.S. patent application Ser. No. 10/______ filed, May 12, 2005, titled SPINAL STABILIZATION, which application is incorporated herein as if set out in full. Another similar technology comprises using conventional pedicle screws.

One conventional pedicle based stabilization system includes a pedicle screw platform threaded into at least a superior and inferior pedicle. Stabilizing cords a placed and spacers inserted between sets of pedicle screws. Once everything is placed, the cords are tightened.

Conventional pedicle based systems, such as the one explained above, provide adequate support, however, any flex of the system is abruptly stopped by either the cord or the spacer. Even if the spacer provides for some flex, the cord provides an abrupt stop in the opposite direction.

Instead of the screw, spacer cord based systems, some pedicle screw stabilization devices provide tracks to allow some movement. For example, the spacer may have elongated slots or tracks on the superior and/or inferior end the spacer to move relative to the pedicle screw, which allows for some relative movement between the superior and inferior vertebrae. The track provides more flex than the spacer/cord systems, but provides abrupt stops in both directions.

Thus, it would be desirous to develop a pedicle screw based spinal stabilization apparatus that provide a dampened stop.

SUMMARY OF THE INVENTION

To attain the advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a pedicle screw based spinal stabilization apparatus is provided. The apparatus uses materials specifically designed to dampen the movement to provide a gentle stop. The apparatus comprises a superior pedicle screw and an inferior pedicle screw. A spacer coupled to the superior pedicle screw and inferior pedicle screw allows compression and expansion of the vertebral bodies. At least a part of the spacer comprises elastic portion that dampens compression and expansion of the spacer to provide a relatively gentle stop to motion

The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention, and together with the description, serve to explain the principles thereof. Like items in the drawings are referred to using the same numerical reference.

FIG. 1 shows a superior view of a vertebral body;

FIG. 2 shows an elevation view of the vertebral body of FIG. 1;

FIG. 3 shows a superior vertebral body and an inferior vertebral body with a pedicle screw based spacer consistent with an embodiment of the present invention;

FIG. 4 shows a pedicle screw and anchor consistent with an embodiment of the present invention; and

FIG. 5 shows a possible shape of a portion of the spacer of FIG. 3.

DETAILED DESCRIPTION

The present invention will now be described with reference to FIGS. 1 to 5. Referring first to FIGS. 1 and 2, a vertebral body 100 is shown for reference. FIG. 1 shows a superior view of a vertebral body 100 (i.e., looking down the spinal column). The vertebral body 100 comprises, among other parts, the pedicles 102, the facets 104, the lamina 106, and the spinous process 108. FIG. 2 shows a side elevation view of vertebral body 100 with a pedicle 102, the facet 104, lamina 106, and spinal process 106.

FIG. 3 shows a side elevation view of a superior vertebral body 302 and an inferior vertebral body 304 (not shown to scale and slightly exploded for ease of reference) with a pedicle screw stabilization device 300. For reference, vertebral bodies 302 and 304 comprise the superior pedicle 306 and the inferior pedicle 308. An intervertebral disk 310 typically exists in intervertebral space 312, but may be removed and/or replace by artificial discs, grafts, or the like.

Device 300 comprises a superior pedicle screw 320 and an inferior pedicle screw 322. A spacer 324 is coupled to the pedicle screws. Spacer 324 includes a elastic/damper portion 326 that allows some expansion and contraction between the vertebral bodies. While shown as a single piece, spacer 324 could be multiple pieces. When multiple pieces are provided, parts may provide dampening in one or both directions as desired. Portion 326 is shown centrally located on spacer 324, but could be located elsewhere and/or be the entire spacer 324. In either direction, the resistance to the motion would increase to provide a relatively gentle stop to the motion instead of the abrupt stop associated with conventional stabilization devices. Spacer 324 could be made our of polymers or other biocompatible material, but it is preferred to construct spacer 324 from shaped memory alloys because of their bone like, elastic qualities at conventional body temperatures. Spacer 324 could be attached to pedicle screws 320 and 322 in any conventional manner. Moreover, while show as a single level stabilization, device 300 could be used for multiple level stabilization.

Optionally, a band 330 can be used to further inhibit flex of the spine. Band 330 can be wrapped about superior pedicle screw 320 and inferior pedicle screw 322. Alternatively, band 330 can be wrapped about other parts of the vertebral body. For example, band 330 could be wrapped about the spinous process of superior vertebral body 302 and the spinous process of the inferior vertebral body 304 as shown in phantom. Band 330 could be any conventional biocompatible material, such as, for example, metals, shaped memory alloys, polymers, PEEK, or the like. Band 330 could be a circular, elliptical, or other shape band or attach similar to a “C” clamp or the like such that band 330 only has a single side.

FIG. 4 shows a top and side view of pedicle screw 400 and anchor 402 to which a spacer 324 may be attached. Anchor 402 has a bone engaging surface 404 and a top 406 opposite the bone engaging 404. A bore 405 extends from the top 406 to the bone engaging surface 404. A channel 408 extends from the top 406 towards bone engaging surface 404. Channel 408 is designed to fit spacer 324. Channel 408 may be open on two sides of anchor 402, similar to a spinal rod system, or open on a single side of anchor 402 (as shown). A setscrew 410 having first threads 412 it threaded onto corresponding threads 414 in bore 405 to couple spacer 324 to pedicle screw 400 and anchor 402. To facilitate the pedicle screws being permanently threaded into pedicles, thread 450 may be coated with bone growth materials 452, as those materials are conventionally understood in the art. Moreover, the pedicle screws may include bone growth channels 454 to promote bone growth through the pedicle screws. Channels 454 may be coated and/or packed with bone growth material. As one of skill in the art would now recognize, the pedicle screws may be similar to bone growth cages. The bone growth should prompt fusing the pedicle screw to the bone.

As mentioned above, spacer 324 and/or portion 326 could be constructed out of a number of materials to provide elastic movement in multiple directions. FIG. 5 shows an optional and possible construction of spacer 324 and/or portion 326 to facilitate expansion and compression of spacer 324. FIG. 5 shows an accordion shape section 500. Section 500 can expand in direction A on application of tension. Section 500 can compress in direction B on application of compression. Using an accordion shape, as section 500 becomes more elongated and/or more compact, the force resisting movement increases to provide a dampening effect. The dampening effect provides a more gentle stop than conventional pedicle screw based stabilization devices.

While the invention has been particularly shown and described with reference to an embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made without departing from the spirit and scope of the invention. 

1. A pedicle screw based spinal stabilization device, comprising: a superior pedicle screw; an inferior pedicle screw; and a spacer coupled to the superior pedicle screw and inferior pedicle screw, the spacer allows compression and expansion of the vertebral bodies and comprises an elastic portion that dampens compression and expansion of the spacer to provide a relatively gentle stop to motion.
 2. The device of claim 1, wherein the spacer is constructed from shaped memory alloy.
 3. The device of claim 1, wherein the elastic portion comprises an accordion shape.
 4. The device of claim 1, wherein the superior pedicle screw and the inferior pedicle screw each comprise an anchor, wherein the anchor includes a bone engaging surface and a top opposite the bone engaging surface, a channel resides in the anchor extending from the top towards the bone engaging surface, the channel being sized to fit the spacer, and a setscrew is threaded into the channel to lock the spacer in the channel.
 5. The device of claim 1, wherein the superior pedicle screw and inferior pedicle screw are separated by multiple vertebrae.
 6. The device of claim 2, wherein the shaped memory alloy is nickel-titanium.
 7. The device of claim 2, wherein the shaped memory alloy has a first shape and a second shape, the first shape providing a first amount of support and the second shape providing a second amount of support.
 8. The device of claim 1, wherein the elastic portion spans the entire spacer.
 9. The device of claim 1 wherein, the elastic portion is located substantially midway between the superior pedicle screw and the inferior pedicle screw.
 10. A pedicle screw based spinal stabilization device, comprising: a superior pedicle screw; an inferior pedicle screw; and a spacer coupled to the superior pedicle screw and inferior pedicle screw, at least a portion of the spacer comprising shaped memory alloy that allows expansion and compression of vertebral bodies.
 11. The device of claim 10, wherein the portion provides motion dampening in both a compression direction and a tension direction.
 12. The device of claim 11, wherein the portion has an accordion shape.
 13. The device of claim 10, wherein the portion comprises the entire spacer.
 14. The device of claim 10, wherein the portion comprises a plurality of portions.
 15. The device of claim 14, wherein the plurality of portions comprises at least a first portion to dampen compressive motion and at least a second portion to dampen expansive motion.
 16. The device of claim 15, wherein the first portion and the second portion are different.
 17. The device of claim 1, further comprising a band coupled to the vertebral bodies.
 18. The device of claim 1, further comprising a band wherein the band is coupled to the vertebral bodies through the superior pedicle screw and the inferior pedicle screw.
 19. The device of claim 18, wherein the band comprises shaped memory alloys.
 20. The device of claim 1, wherein the superior pedicle screw carries a bone growth material.
 21. The device of claim 20, wherein the inferior pedicle screw carries the bone growth material.
 22. The device of claim 1, wherein the superior pedicle screw comprises at least one bone growth channel.
 23. The device of claim 22, wherein the inferior pedicle screw comprises at least one bone growth channel. 